The influence of the interface coefficient of friction upon the propensityto judder in automotive clutches

This paper presents an investigation of the driveline torsional vibration b ehaviour, referred to as judder, which takes place during the clutch engage ment process, particularly on small trucks with diesel engines. A non-linea r multibody dynamic model of the clutch mechanism is employed to study the effect of various clutch system and driveline components on the clutch actu ation performance. The paper demonstrates that judder is affected by drivel ine inertial changes, variation in the coefficient of friction, mu, of the friction disc linings with slip speed, upsilon, and the loss of clamp load. The results of the simulations show that various friction materials with d ifferent mu-upsilon characteristics produce torsional self-excited vibratio ns of the driveline. The results also show that loss of clamp load relating to the speed of clutch actuation also contributes to judder. Furthermore, it is shown that the simulation results conform closely to the experimental findings.